Helicopters are unique in their ability to operate in vertical, hover and translational modes of flight. The price exacted by this multiple flight mode capability, however, is that limits are imposed on the design options available for each flight regime, which results in less than optimum efficiency for each. The main rotor must operate in a highly complex and unsteady aerodynamic environment with tight coupling of the rotor/airframe aerodynamics, dynamics, and structural characteristics. The complex aerodynamic environment leads to high noise, especially during landing when blade vortex interactions cause elevated acoustic energy to be transmitted from the aircraft. The tight coupling of the main rotor to the airframe causes high levels of vibration to be transmitted to the airframe, which adversely affects passenger comfort and pilot endurance; and the differential airspeed experienced by the advancing and retreating blades during translational flight limits the top speed of a helicopter.
In a conventional helicopter control system, the longitudinal and lateral rotor blade cyclic pitch control as well as the average rotor blade pitch (collective) are transmitted the rotor blades by means of a rotor blade swashplate mechanism. Pilot control inputs are translated into elevation and tilt angle of the non rotating swashplate which are transmitted to the rotor blades by means of pitch links attached at their lower ends to a rotating swashplate and at their upper ends to the leading or trailing edges of the blades near their attachment to the main rotor hub. Conventional helicopter control systems, thus, are unable to provide any control inputs other than collective and once-per-revolution cyclic pitch adjustments of the rotor blades. It has been suggested that the aerodynamic forces that contribute to the noise, vibration and speed limitations inherent in helicopter flight could be compensated or negated if it were possible to provide aerodynamic control inputs that were decoupled from the cyclic pitch controls and thus could be provided at arbitrary frequencies. Independent control of these aerodynamic forces could, of course, be achieved through the use of active control surfaces on the rotor blades themselves, however, because the active control surfaces and their servo mechanisms would have to be housed within the main rotor blades, numerous design limitations have heretofore prevented practical implementation of such rotor blade control surfaces. Among the most challenging of the design constraints is that additional weight of any such control surface and its servomechanism must be small. Otherwise the total weight of the rotor blade, which must be supported by the main hub, becomes unacceptably high. Additionally, the actuator must be capable of withstanding the high centrifugal forces and flapping accelerations experienced by the rotor blades. Accordingly, what is needed to implement the aforementioned dynamic active helicopter blade control is a helicopter rotor blade equipped with a control surface, such as a trailing edge flap, coupled to a lightweight, rugged actuator suitable for mounting within the profile of a helicopter rotor blade.